It has been believed that an all-digital, electrically powered servo if ever conceived should provide significant advantages over the currently used electrohydraulic servo. The advantages include the following:
1. Lower overall system complexity and cost. The opportunity exists to simply expand the electrical power system (which must be available in any case) to provide the added power instead of adding a hydraulic power system for this purpose. PA0 2. Repeatable, "text book" quality performance. PA0 3. Testability. Simple electric power turn-on, followed by computer-oriented self-test routines should suffice. PA0 4. Potential for reduced energy consumption. PA0 5. An inherent fail-safe power unit. Primary failures result in failure to increment. PA0 6. An unprecedented high level of reliability in the power unit by reason of the use of simple, high force incrementers.
Other application-specific advantages should surface. For instance, in military aircraft flight control systems, a control-by-wire/power-by-wire concept would augment the flexibility of modern fly-by-wire control systems but omit the weight and the vulnerability of the hydraulic supply and distribution system. In computer aided manufacturing, an interface to a numerically controlled machine or robot which is all-electric and all-digital is likewise a highly desirable feature.
There are host of servos in operation which are labeled "digital," but an examination of the power units which is part of the overall servo reveals that they are analog. These servos require some form of digital to analog conversion which leaves them out of the category of "all-digital."
A servo having a stepper motor as the power unit qualifies as "all-digital" and "electrically powered" but theseservos either exhibit a high resolution and high load capacity but lack speed, or they exhibit speed but lack resolution and load capacity. Recently developed high speed, high force solenoids, however, provide the basis for meeting the joint requirement of speed and force if it were possible to effect bilateral incrementation in the presence of reversible loads. The proposed system accomplishes this in a manner unlike anything known in servo technology.